Piper explains his position on alcohol and church membership:
When I came to Bethlehem Baptist Church over [three] decades ago, this was one of the first controversies I had to deal with. We survived it and are he better for it. I think what I learned may be helpful.
Among Baptist and other congregationally governed churches, the local church constitution generally contains an affirmation of faith and church covenant. The church covenant describes a core set of Biblical expectations relating to how members live; while the affirmation of faith describes a core of Biblical expectations relating to what members believe. As a general rule, therefore, the expectations of the church covenant, along with the affirmation of faith, function as prerequisites for church membership.
Many congregationally governed churches have a sentence in their church covenants which goes something like this: ‘We engage to abstain from the use and the sale of intoxicating liquors as a beverage.” In principle, therefore, these churches exclude all persons except teetotalers from church membership. . .
I am persuaded that such a regulation from church membership falls into the category of legalistic exclusivism and stands under the judgment of the apostolic word in Scripture. This is my persuasion even though I am a total abstainer myself and believe total abstinence is a wise and biblically defensible way of life for our day.
John Piper, Brothers, We Are Not Professionals (Nashville, TN: Broadman and Holman, 2002), 151-152 (emphasis and paragraphing mine).